Stealth Orifice

ABSTRACT

The present invention regards a surface controlled device designed for injection of fluids in a well bore, typically Man offshore well bore for petroleum production and gas injection/gas lift system for fluid injection. The device comprises a outer hollow housing ( 1 ) with at least one inlet and outlet and an internal body ( 2 ) moveable in a longitudinal direction within the outer N housing ( 1 ). An inlet, in form of a variable orifice, is connected, through a mainly longitudinal bore of the internal body, with at least one slot. The present invention will give a fluid exiting the device with a minimal amount of energy or pressure loss over the device.

The present invention regards a device for injection of fluids in a wellbore, typically a well bore for petroleum production, and in particularfor a gas lift valve, which is used to inject high pressure gas into atubing string disposed in a well bore for the purpose of aerating and/ordisplacing the liquid in the tubing string, thereby lifting the liquidto the surface or top of the well bore.

In producing hydrocarbons, including water, oil, oil with entrained gasand gas, from a geological formation, natural pressure in the formationis employed to lift the hydrocarbons upwards to the ground surface. Thispressure can decrease over the life time of the well and will requireassist to improve lift, where this can be done by artificial supplyingof energy to the liquid or medium in the production tubing. One knownmethod to increase lift is to inject a medium into the productiontubing. This injection is usually done by forcing the medium down theannulus between the production tubing, which tubing conductshydrocarbons to the surface, and the (steel) casing of the well, furtherthrough a device for injection and into the production tubing. Here themedium will mix with the hydrocarbons, thus reducing the overall densityof the mixture, which will lead to that lift in the well bore isimproved. The medium that is to be injected into the production tubingis usually gas or water, although other constituents such as wellstimulation fluids etc. also can be used.

The properties and/or flow of the injected gas or water have however tobe controlled, as parameters like pressure, speed, density etc arecritical in order to obtain most favourable conditions in the productiontubing. The two most common types of gas or water control devices thatare employed to control the injected medium into the production tubingare gas lift valves and orifices.

Other production enhancement method exists through installation of subsea or sub surface electrically driven pumps or other elements to assistthe production flow out of the production tubing.

The basic idea for all such methods is to drive more hydrocarbons out ofreservoir.

Several different principles of operating a gas injection valve areknown, one of these is based on the venturi principles, for instance asdescribed in WO 2004/092537 A1. One another approach is to have acentral stem with outer sealing surface and a through going flow betweenan outer housing and the central stem across the sealing surfaces, forinstance as described in CA 02461485 A1.

A common problem that arises in connection with gas lift is flowinstability where this is characterized by large flow rate and pressurefluctuations that can cause severe separation and gas injectiondistribution problems. These gas lift instabilities are associated withlow productivity wells that have a large annulus and/or produce at lowgas injection rates. In addition, gas lift instability can also occur ifthe flow through a gas flow control device is in the sub critical flowrange. In the critical or sonic flow range, the production pressure doesnot affect the gas flow rate through the device and flow instabilitycannot occur. The gas flow control device may be preferred to be incritical or sonic flow range with the least possible pressuredifferential across the device.

In order to prevent flow instabilities, one can increase the gasinjection rate and or choke the production of the hydrocarbons at thewellhead. This will however result in that the gas injection is to beperformed above the most economical rate and the choking reduces rate ofproduction. Thus, there are economical objections to the usual measuresfor managing with gas lift instability.

It is therefore an object of the present invention to minimize andpossibly alleviate these problems.

It is further an object of the present invention to provide a devicethat eliminates or minimizes flow instability.

There is also an object of the present invention to provide a devicewith a low operating pressure difference.

These aims are achieved with a device for injection of fluid accordingto the invention as defined in the enclosed independent claim, whereembodiments of the invention are given in independent claims.

The present invention is intended to provide a device for altering flowcharacteristics that eliminates or minimizes flow instability, where thedevice comprises an outer hollow housing with an internal body (aso-called dart). The internal body is movable in the longitudinaldirection of the outer housing and comprises an internal bore. In orderto permit the fluid to flow through the device, both outer housing andinternal body is formed with at least one inlet and outlet, where theinternal body restrain the passage through the device in a closedposition. When a pressure differential over the device at a given valueis large enough, the internal body will be forced to move to an openposition. In this position the outlets of the internal body and theouter hollow housing correspond to each other, thereby letting the fluidwhich is to be injected in the production tubing, through.

This pressure differential may be a fluid pressure operating on surfacesof the internal body, which surfaces may be exposed to different fluids.These fluids may be well fluids on one or more surfaces for operatingthe device or injections fluid on one surface and well fluid on anothersurface or combinations. According to an aspect the pressuredifferential across the internal body may be assisted by at least onepredetermined pressure balanced elastic element to open and close thedevice.

The inlet of the internal body is connected to the outlet of theinternal body through the internal bore, where the inlet is in form of avariable orifice. With variable orifice it should be understood in thisapplication that the orifice is changing in form over its length whenseen in the longitudinal direction of the device. The orifice is furthera separate unit which can be mounted to the internal body through athreaded connection thereby following the movement of the internal body,or the orifice could be fastened to the internal body by differentadhesives, locking ring(s), set screw(s) etc.

According to an other embodiment the orifice can be mounted or fastenedto the inner surface of the outer hollow housing by for instanceadhesives, threaded connections etc.

In order to achieve a critical flow through the device, the orifice hasa variable design over its length. In a first embodiment the orifice isdivided into an inlet section, a middle section and an outlet section,where the inlet and outlet sections have form of a rectilinear truncatedcone. The length of each section, when seen in the longitudinaldirection of the device, can be different, where this will depend on themedium to be used in the device etc. The medium used will also affectthe shaping of the different sections, where this for instance can givethat the inlet section has a wider opening angle than the outletsection. The inner surface (walls) of the inlet and outlet sections forman angle to a horizontal line, where this line is an imagined extensionof the inner surface of the middle section.

The inner surfaces of the orifice will give minimal resistance to theflow of medium as the medium run through the orifice. This may beachieved by machine the inner surfaces of each section or by coating theinner surface with a coating.

The truncated cone can in alternative embodiments of the presentinvention have sides that are curvilinear, for instance convex orconcave or any other form, where both the inlet and outlet section canbe shaped in same form. It can also be imagined that the inlet andoutlet section can be combinations of the above described forms, forinstance can the inlet section have a concave form while the outletsection can have a convex or rectilinear inner surface.

The middle section of the orifice can in a first embodiment of theinvention have an inner uniform and rectilinear surface, which isparallel with the surface of the longitudinal bore of the internal body.The cross section of the middle section can further be smaller than thecross section of the longitudinal bore. The inner surface of the middlesection can also have other forms, for instance an expanding orincreasing form, curvilinear etc.

It is also possible that a center axis of the middle section isdisplaced compared with a center axis of the longitudinal bore, wherethis will give that the inner surface of the middle section that ismisaligned, but parallel, with the inner surface of the internal bore.

In yet another embodiment an end termination of the outlet section canbe extended a length into the longitudinal bore. This can result in, asdescribed above, that the orifice do not have to be mounted to theinternal body, but can in appropriate ways be connected to the innersurface of the outer housing. The end termination may for instance be asleeve that is mounted to the outlet section where the sleeve has adiameter that is slightly smaller than the inner diameter of theinternal bore. This will cause that only the internal body is moved whenthe pressure is large enough to move it to an open position.

The orifice unit can be manufactured from any suitable material, forinstance in a metallic or other casted/moulded or ductile material. Askilled person will know how this can be done.

Even though the device above is referred to as a gas injection device,it is to be understood that the principles of the device may also beused for other kind of injection valves. This may for instance be whenthe device is used for injection of other constituents such as wellstimulation fluids, cutting injection, water injection etc.

These features of the present invention will provide a device where theflow path of the injection fluid is substantially less tortuous thanother known gas injection valves due to more direct flow through thebore in the internal body and directly out through the slots.

This also gives less pressure losses across the valve. By designing theinlets, orifice, outlets and the slots of the device, one could achievethe desired effect with regard to flow pattern and cavitations. Thepresent invention is also a simplified device with few elements,compared with the majority of other known injection valves. This gives amore reliable device as well. The present invention also has arelatively large flow area through the device, compared with themajority of other known injection valves of similar size.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred non-limiting embodiments of the invention, asillustrated in the accompanying drawing, where

FIG. 1 shows a cross section of a first embodiment of the presentinvention.

In FIG. 1 is shown a first embodiment of a device according to theinvention, where the device is used as a gas lift valve which is to bepositioned in a well stream. A skilled person will understand how thisis done and this is therefore not described in this application.

In the FIG. 1 the device, normally used as a gas lift valve, comprisesan outer hollow housing 100 with an internal body 2 movable within theouter hollow housing 100. The internal body 2 is movable between aclosed and an open position of the device, and is in this embodimentshown in an open position. The outer hollow housing 100 in thisembodiment is manufactured of a main part 1 and a nose 11. The nose 11is connected to the main part 1 with suitable means, for instance by athreaded connection. In the outer hollow housing 100 are arranged one ormore inlets 14 for injection fluid, where these inlets 14 are arrangedaround the circumference of the outer housing 100. In the shownembodiment the outer hollow housing 100 is arranged with four slots, twoand two placed above each other. The inlets 14 are in contact with aninjection fluid source (not shown). On the opposite end of the outerhousing 100, that is in the nose 11, there are arranged one or moreoutlets 5, these outlets 5 also being placed around the circumference ofthe nose 11.

From the inlets 14 the injection fluid is flowing into an internal void15 of the outer hollow housing 100 through an orifice 4 and into aninternal bore 3 of the internal body 2. The orifice 4 in this embodimentis a separate unit, but is mounted by a threaded connection 7 on anoutside of one end of the internal body 2, and forms therefore part ofthe internal bore 3. The bore 3 stretches in the longitudinal directionof the internal body 2 from an end of the internal body 2 and nearly tothe other end of the internal body 2. The injection fluid willthereafter in an open position of the valve flow trough one or moreslots 6 leading from the internal bore 3 to the outside of the internalbody 2. In the shown example four slots 6 are arranged around thecircumference of the internal body 2, but there may of course be less ormore slots 6 arranged around the circumference of the internal body 2.In an open position of the valve the slots 6 of the internal body arealigned with outlets 5 in the outer hollow housing 100, thereby leadingthe injection fluid out into the process fluid flow. The injection fluidwill in this open position of the device therefore have a flow patternwith a minimum amount of bends and or other obstructions, where thiswill result in minimal pressure losses across the valve.

As can be seen in the figure, the internal body 2 comprises an annular,valve sealing surface 19, with a mainly conical shaped surface. Thissurface 19 is arranged close to an end of the internal body 2 with theend of the conical shaped surface 19 with the larger diameter, furthestaway from the slots 6 of the internal body 2. The slots 6 are arrangedclose to an end of the internal body 2, and the surface 19 closer to thesame end of the internal body 2. The sealing surface 19 of the internalbody cooperates with a valve seat 20 arranged in the outer hollowhousing 100. The valve seat 20 in the outer hollow housing 100 isarranged on the relative speaking other side of the slots 6 and outlets5, where these are aligned in an open position of the valve, comparedwith the sealing surface 19 of the internal body, seen in thelongitudinal direction of the device. In a closed position, the internalbody 2 is moved relative the outer hollow housing 100 so that thesealing surface 19 is abutting the valve seat 20, giving a sealed, metalto metal seal for the valve. In this closed position the slots 6 of theinternal body 2 will be positioned within the valve and the outlets 5 ofthe outer hollow housing on the other side of the interaction betweenthe sealing surface 19 and the valve seat 20. The sealing surface on theinternal body 2 and the valve seat 20 in the outer hollow housing 100will in an open position of the device be at least partly covered by theother element of the device, outer hollow house 100 and internal body 2respectively.

The orifice 4 have an important purpose in the device and that is togain a critical flow for the injection medium, where this is obtained byseparating the orifice 4 in three different sections, namely an inletsection 8, a middle section 9 and a outlet section 10, leading theinjection medium into the internal bore 3. Although it in the figure isshown that the orifice 4 is consisted of three sections it should beunderstood that the orifice 4 also could be divided into more sections.The sections 8, 9, 10 are connected with each other and can be made bymachining the orifice 4 unit or by moulding. A skilled person will knowhow this could be done.

In this embodiment the length of the different sections 8, 9, 10 in theorifice 4, when seen in the longitudinal direction of the device, aredifferent, but they can also be of equal lengths. The inlet section 8and the outlet section 10 have a form of a truncated and rectilinearcone Inner surfaces or walls of the inlet section 8 and outlet section10 form an angle 13 with a horizontal line 12, where this horizontalline 12 is an imaginary prolongation of the inner surface of the middlesection 9. This angle 13 (opening angle) may for instance be up toeighty degrees, and in the shown embodiment the opening angle of theinlet section 8 is larger than the opening angle of the outlet section10. The inlet section 8 will further narrow in to the same form or crosssection as the middle section 9 has.

The middle section 9, that connects the inlet section 8 and the outletsection 10, is shaped as a bore, where the inner surface is uniform andrectilinear. A centre axis 21 of the middle section 9 coincides with acentre axis 21 of the internal bore 3, and the inner surface of themiddle section 9 is therefore parallel with the inner surface of theinternal bore 3. The middle section 9 has further a smaller diameterthan the internal bore 3.

The outlet section 10 will have its smallest cross section where it isconnected to the middle section 9, and will thereafter widen out whenseen in the longitudinal direction of the device, until it connects withthe internal bore 3.

Cross sections taken along planes perpendicular to the centre axis 21 ofthe orifice 4 have a circular form. Other geometries can however bepossible.

In one other embodiment of the present invention, the orifice 4 still isformed as a truncated cone, but the inner surfaces or walls of the inletsection 8 and outlet section 10 are concavely shaped.

When the device is used as a gas lift valve, pressurized gas atinjection pressure enters device through inlets 16 and into the internalvoid 15 of the outer hollow housing 100, and flows thereafter throughthe orifice 4. The pressurized gas will gain an increase in flowvelocity and reduction in pressure through the inlet section 8 of theorifice 4, where these parameters are “stabilized” in the middle section9 of the orifice 4; over the outlet section 10 the flow velocity for thepressurized gas will decrease while the pressure will increase until thepressurized gas enters the internal bore 3, through which the parametersagain are “stabilized”. The gas is then discharged through slots 6 andoutlets 5 at production pressure, and passes into the production tubing.

Only elements related to the invention is described and a skilled personwill understand that an outer hollow housing or internal body may beformed in one unit or be comprised of several connected elements, andthat the inlets have to be connected to a source of fluid to beinjected, that there should be appropriate attachment devices forattaching the valve within a process fluid stream, and that there ofcourse will be arranged for instance sealing element between severalelements as a standard. The skilled person will also understand that onemay make several alterations and modifications to the described andshown embodiments that are within the scope of the invention as definedin the following claims.

1. Device for injection of fluids in a process fluid for use in a wellbore, comprising an outer hollow housing with at least one inlet and oneoutlet and an internal body movable in a longitudinal direction withinthe outer hollow housing and hereby forming a closed and open state ofthe device, where the movement of the internal body is operated bypressure differential across the device, wherein the internal bodyfurther comprises a mainly longitudinal bore with an outlet in the formof at least one slot from the bore to an outside of the internal bodyand that the internal bore at an inlet comprises an orifice with avariable cross section along the longitudinal axis of the bore. 2.Device according to claim 1, wherein the orifice is a separate unit,mounted to the internal body by a threaded connection.
 3. Deviceaccording to claim 1, wherein the orifice is divided into an inletsection, a middle section and an outlet section, where the inlet andoutlet sections have a form of a truncated cone.
 4. Device according toclaim 3, wherein the sides in the truncated cone are rectilinear. 5.Device according to claim 3, wherein the sides in the truncated cone arecurvilinear.
 6. Device according to claim 3, wherein the inlet sectionhas a wider opening angle than the outlet section.
 7. Device accordingto claim 3, wherein the middle section has an inner uniform surfacewhich is mainly parallel with the longitudinal bore of the internalbody, and where a cross section of the middle section is smaller than across section of the longitudinal bore.
 8. Device according to claim 3,wherein an end termination of the outlet section is extended a lengthinto the longitudinal bore.
 9. Device according to claim 3, wherein thecenter axis of the middle section is misaligned according to a centeraxis of the internal bore.